Apparatus for connecting an image sensor and an optical unit to a circuit board so that they are properly aligned

ABSTRACT

An arrangement for an image scanning unit (1) includes a semiconductor package (2) so arranged as to generate electrical signals corresponding to an image incident upon the light-sensitive surface (2a) of the package and so arranged as to be connected to a circuit (5) by soldering its contact legs (2b) to the circuit board (5). Also present are an optical system arranged in a holder (3) for projecting the image to be scanned onto the aforementioned light-sensitive surface (2a) and a mounting plate (4) positioned between the semiconductor package (2) and the circuit board (5). Finally, devices (3a, 3b, 4a) are also present for joining together the holder (3) and the mounting plate (4) and for ensuring correct mutual alignment between the semiconductor package (2) and the optical system.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an arrangement for am image scanningunit comprising a semiconductor package so arranged as to generateelectrical signals corresponding to an image incident upon thelight-sensitive surface of the package and so arranged as to beconnected by soldering to a circuit board, an optical system arranged ina holder for projecting the image to be scanned onto the aforementionedlight-sensitive surface, a mounting plate positioned between thesemiconductor package and the circuit board, and devices for joiningtogether the holder and the mounting plate and for ensuring correctmutual alignment between the semiconductor package and the opticalsystem.

2. Description of the Related Art

An arrangement of this kind is previously disclosed through U.S. Pat.No. 4,594,613. The mounting plate is attached in this case to the holderfor the optical system by means of screws and pins, which projectoutwards from the holder and interact with holes in the mounting platein order to ensure the desired alignment between the semiconductorpackage and the optical system. The previously disclosed arrangement hasa comparatively bulky construction and uses many detail components whichdemand a relatively long assembly time; in order to be able to fix theholder to the mounting plate with screws, or vice versa, openings arealso required in the actual circuit board. Ensuring that the holder iscorrectly aligned relative to the semiconductor package, as brieflydescribed above, means that the accuracy of the alignment may bejeopardized.

SUMMARY OF THE INVENTION

The object of the present invention is to make available an arrangementof the kind referred to by way of introduction, in which elimination ofthe above-mentioned disadvantages has been effected and has been madepossible in that in order to ensure correct alignment between theoptical system and the light-sensitive surface of the semiconductorpackage in the longitudinal direction of the semiconductor package, theaforementioned devices comprise a projection projecting from the holderin such a way, when the unit is assembled, that it engages between twoof the contact legs of the semiconductor package, and that for ensuringcorrect alignment in the transverse direction of the semiconductorpackage and in a direction normal to the light-sensitive surface, theaforementioned joining devices comprise snap elements capable ofinteracting with one another arranged on the holder and on the mountingplate.

A desired alignment accuracy tolerance between the optical system andthe light-sensitive surface of the semiconductor package is achievedthrough the characteristic features of the invention in that thelocation of the holder is achieved by means of the semiconductor packageitself or, rather, with two of its contact legs. In addition, aspace-saving, rapid, reliable and simple joint is obtained between theholder and the mounting plate.

In accordance with one particular characteristic of the invention, thesnap elements in one preferred embodiment are arranged along two linesrunning parallel to one another and to the longitudinal edges of thesemiconductor package and lying in areas close to them.

BRIEF DESCRIPTION OF THE DRAWING

The invention is described in greater detail below with reference to theaccompanying drawing, in which FIG. 1 illustrates an exploded view ofthe invention in perspective view. FIG. 2ashows the arrangement inaccordance with the invention installed, and FIG. 2b is a detailed viewshowing a projection which ensures correct alignment between thelight-sensitive surface of a semiconductor package and an opticalsystem, by means of which an image is projected onto the aforementionedsurface. FIG. 3a shows the arrangement in accordance with the inventionshown in FIG. 2a in side view, and FIG. 3b is an enlarged partial viewof FIG. 3a, which shows snap elements by means of which a holder for theoptical system is fixed to a mounting plate for the holder.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The designation 1 is used in the drawing generally for an image scanningunit comprising a semiconductor package 2 with a light-sensitive surface2a, a holder 3 for an optical system (not shown in the drawing) forprojecting onto the light-sensitive surface 2a an image which is to bescanned, a mounting plate 4 and a circuit board 5.

The semiconductor package has contact legs 2b which carry electricalsignals corresponding to the image incident upon the light-sensitivesurface 2a when the image scanning unit is being used, and which areintended to be connected in the conventional manner to a conductivepattern on the circuit board 5. The contact legs 2b are inserted forthis purpose into holes 5a in the circuit board 5 and are soldered inplace to the conductive pattern. The mounting plate 4 is so arranged asto be positioned between the semiconductor package 2 and the circuitboard 5 in the space which is conventionally present between a circuitboard and a semiconductor package of this kind when it is soldered inplace on the circuit board.

Rapid and reliable joining of the holder 3 to the mounting plate and, atthe same time, accurate alignment of the optical system relative to thelight-sensitive surface 2a in the transverse direction of thesemiconductor package 2 and in a direction normal to the surface 2a areachieved in accordance with the invention by means of snap elements 3b,4a interacting with one another arranged on the holder 3 and on themounting plate 4 and preferably integral with them. The manner in whichthese snap elements 3b, 4a interact can be appreciated most clearly fromFIGS. 3a, 3b.

The holder 3 exhibits on its surface facing the semiconductor package 2a recess 3c into which the semiconductor package 2 fits. When thepackage 2 is introduced into the recess 3c and rests against its bottom,the edges 3cl, 3c2 of the recess 3c form guide edges for thelongitudinal edges of the semiconductor package 2. When the arrangementis installed, the internal surfaces of the snap elements 4a belonging tothe mounting plate 4 and facing towards the contact legs 2b also touchcorresponding contact legs 2b. Very stable and reliable alignment isthus achieved between the component parts of the arrangement.

An image scanning unit 1 in accordance with the invention is installedas follows: first the semiconductor package 2 is attached to themounting plate 4, in conjunction with which a number of the contact legs2b of the semiconductor package 2, more specifically those which aresituated in association with the snap elements 4a, are caused to passthrough transcurrent holes 4b in the mounting plate 4. The rear surface2c of the semiconductor package 2 facing away from the light-sensitivesurface 2a now comes into contact with the top surface 4c of themounting plate. The semiconductor package 2 together with the mountingplate 4 is then assembled with the circuit board 5, whereupon thecontact legs 2b are soldered in place on the circuit board 5 in theconventional manner.

The holder 3 can now be installed. It is essential to make sure that theprojection 3a is introduced between two selected contact legs 2b at thesame time as the snap elements 3b, 4a are brought into engagement withone another. Once this has occurred, an edge area of the light-sensitivesurface 2a will lie against a surface (not shown in the drawing)corresponding to the underside of the holder 3. Direct and accuratealignment of the holder, and thus of the optical system arranged in theholder, relative to the light-sensitive surface is achieved in this way.

I claim:
 1. An arrangement for an image scanning unit comprising:asemiconductor package, so arranged as to generate electrical signalscorresponding to an image incident upon a light-sensitive surface of thepackage, and so arranged as to be connected to a circuit board bysoldering its contact legs to the circuit board, the semiconductorpackage extending generally in a first, longitudinal, direction and asecond, transverse, direction, and the light-sensitive surface extendingin said longitudinal and transverse directions; an optical systemarranged in a holder for projecting the image to be scanned onto thelight-sensitive surface; a mounting plate positioned between thesemiconductor package and the circuit board, and devices for joiningtogether the holder and the mounting plate and ensuring correct mutualalignment between the semiconductor package and the optical system;wherein, for ensuring correct alignment between the optical system andthe light-sensitive surface of the semiconductor package in thelongitudinal direction of the semiconductor package, said joiningdevices comprise a projection projecting from the holder in such a waythat, when the unit is assembled, it engages between two of the contactlegs of the semiconductor package; and wherein, for ensuring correctalignment in the transverse direction of the semiconductor package andin a direction normal to the light-sensitive surface, said joiningdevices comprise snap elements, capable of interacting with one another,arranged on the holder and on the mounting plate.
 2. An arrangement asclaimed in claim 1, wherein the holder exhibits, on its surface facingthe semiconductor package, a recess into which the package fits, theedges of which recess form guide edges for edges of the semiconductorpackage extending in the longitudinal direction.
 3. An arrangement asclaimed in claim 1, wherein the holder exhibits, on its surface towardsthe semiconductor package, a recess into which the package fits, theedges of which recess form guide edges for the longitudinal edges of thesemiconductor package.
 4. An arrangement as claimed in claim 1, whereinthe surfaces of the snap elements arranged on the mounting plate andfacing towards the contact legs also touch corresponding contact legs.